The 500 V laterally diffused metal oxide semiconductor (LDMOS) has both the characteristic of high voltage and current of a discrete device, and the advantage of high-density intelligent logic control of a low-voltage integrated circuit, allowing a single chip to achieve the function that is originally achieved by multiple chips, thereby greatly reducing the area and cost and improving the energy efficiency, in line with the development of miniaturization, intelligence and low energy consumption of modern electronic devices.
As a key parameter for examining the 500 V devices, the breakdown voltage is particularly important. The prior art can promote depletion of the drift region by forming a PTOP layer on the drift region, thus reducing the surface field (Resurf) effect. As shown in FIG. 1 is a schematic view of the structure of an existing NLDMOS device. An N-type deep well 2 is formed on a silicon substrate 1, a P well 4 is spaced from a drift region and also surrounded by the N-type deep well 2, field oxide 3 is formed on the N-type deep well 2, a gate is composed of a gate oxide layer 6 and a polysilicon gate 7, a source region 8b is formed in the P well 4 and self-aligned with the polysilicon gate 7, a P well lead-out region 9 is formed on the P well 4 and composed of a P+ region, and a drain region 8a is formed on the drift region and self-aligned with a side of the field oxide 3. A polysilicon field plate 7a is formed at a side of the field oxide 3 adjacent to the drain region 8a, with both the polysilicon field plate 7a and the polysilicon gate 7 formed by photoetching the same polysilicon layer. An interlayer film 10 covers the region of the device on the bottom, with the source, drain and gate of the device led out through a contact hole and a front metal layer 11. A PTOP layer 5, formed on the drift region and also on the bottom of the P well 4 at the side of the source region 8b, is able to promote depletion of the drift region, reduce the surface field, and finally increase the breakdown voltage of the device.